Electrodeposition of palladium



United States Patent ()ffice 3,530,05- Patented Sept. 22, 1970 U.S. Cl. 204-47 14 Claims ABSTRACT OF THE DISCLOSURE Electrolysis or electrodeposition is carried out with an aqueous neutral or alkaline bath containing a palladium compound and an ammonium salt of a weak organic acid which does not form an insoluble compound with the palladium compound.

This invention relates to improvements in and relating to the electrodeposition of palladium onto a basis metal.

Palladium is usually deposited from a plating bath or electrolyte which comprises an aqueous solution of a palladium compound and generally also contains ammonia to render the bath slightly alkaline.

For example, palladium plating baths based on palladium diammino-dinitrite Pd(NH (NO commonly known as the P salt or palladium tetrammino-dinitrate, Pd(NH (NO have been proposed. Such baths are usually operated at a pH of from -5 to 9 and a temperature of from about 50 C. to 95 C.

Deposits of palladium obtained by the use of plating baths as at present known, have, for various reasons, not proved entirely satisfactory and certain disadvantages are inherent in the use of the aforesaid baths.

More recently, it has been proposed to provide a palladium plating bath, particularly suitable for plating printed circuit boards, which comprises an aqueous solution containing in addition to palladium ions, and ammonium ions, also a source of sulphamate ions, for example, the bath may be based on the reaction of the known P salt, above referred to, with sulphamic acid or ammonium sulphamate, to form a compound the exact nature of which is not yet definitely known.

The bath is stated to offer advantages over the conventional baths and to be operable at, or near, room temperature.

The object of this invention is to provide a novel palladium plating bath or electrolyte which is stable, can be operated at a low temperature and by means of which substantially pore-free and heavy deposits of palladium can be consistently obtained.

According to one feature of this invention, a plating bath or electrolyte for the electrodeposition of palladium comprises an aqueous neutral or alkaline solution containing a palladium compound and an ammonium salt of a weak organic acid, which does not form an insoluble compound with the palladium compound.

According to another feature of the invention, a method of electrodepositing palladium comprises electrolysing an electrolyte comprising an aqueous neutral or alkaline solution containing a palladium compound and an ammonium salt of a weak organic acid which does not form an insoluble compound with the palladium compound.

According to yet another feature of the invention, a method of electrodepositing palladium on a basis metal comprises depositing on said basis metal palladium metal from a plating bath or electrolyte comprising an aqueous neutral or alkaline solution containing a palladium compound and an ammonium salt of a weak organic acid which does not form an insoluble compound with the palladium compound.

The palladium compound employed in carrying out the invention is preferably palladium-diammino-dinitrite.

but other palladium compounds, such as palladium-tetrammino-nitrate, Pd(NH (NO or palladium chloride may also be used.

The organic acid salts may advantageously be chosen from the following ammonium salts, namely, ammonium tartrate, ammonium oxalate, ammonium citrate, ammonium formate and an ammonium salt of ethylene diamine tetra-acetic acid. Of these salts, the applicants have found that very satisfactory results are obtained with the use of ammonium formate.

Ammonia is preferably included in the solution to give a pH of from 7 to 10, preferably 8-9, the brightness of the deposit in general increasing with increase in the pH. The solution should, preferably, be free of cyanide ions.

The baths of the invention should preferably be operated at a temperature of 15-75 C. It will be found advisable, however, in the case of a bath containing ammonium formate, not to operate at :a temperature of over 40 C. over a period as, in that event, the palladium is liable to precipitate out and be deposited chemically. The current density at which the baths are operated may vary from 1 amp/sq. ft. to 500 amps/ sq. ft.

The following are examples of suitable plating baths in accordance with the invention and operating conditions therefor, it being clearly understood that the invention is in no way limited to, or by, these examples.

In the examples in which the palladium compound used is palladium diammino-dinitrite Pd(NH (NO the plating bath is made by dissolving the palladium salt in ammonia at the rate of 2 mls. of 0.880 ammonia per gram of palladium (2.175 grams of Pd(NH (NO correspond to 1 gram of Pd), and. an equal amount of water. The organic acid salt is then added and the pH adjusted as required.

EXAMPLE I Palladium diammino-dinitrite Pd(NH (NO -24 g./l.

(representing 11 g./l. of Pd).

Ammonium tartrate-- 50' g./l.

Water to 1 litre.

This bath should be operated at a current density of 6 amps/sq. ft. at a temperature of 30 C. The pH of the bath was adjusted to 8.5. A bright deposit of palladium was obtained.

EXAMPLE II Palladium diammino-dinitrite Pd(NH (N0 --24 g./l.

(=11 g./l. of Pd).

Ammonium oxalate-50 g./l. Water to 1 litre.

This bath should also be operated at a current density of 6 amps/sq. ft. at a temperature of 30 C. The pH of 3 the bath was adjusted to 8.5. A bright deposit of palladium was obtained.

EXAMPLE III Palladium diammino'dinitrite Pd(NH 2 (N -24 g./l.

4 EXAMPLE VIII Palladium acetate Pd(CI-I COO) 21.1 g./l.

=10 g./l. Pd). Ammonium oxalate-50 g./l.

Water to 1 litre.

(=11 g./l. of Pd). I A i citrate--60 g./l. The palladium acetate was first dissolved, by warmmg Water to 1 litre. 1n ammonia to form Pd(NH (CH COO) and the pH of The operating conditions for this bath may be the same g g lgg g gg zg ii i to 8 7 with the addl Ion as those of the prevlous examples This bath produced a dull deposit of a thickness of EXAMPLE IV 0.00019 inch when operated at a current density of 6 Palladium diammino-dinitrite Pd(NH (NO 24 g./l. 22252331 z g gf g of 30 and gave a :11 g./l. of Pd). y Ammonium formate-SO g./l. 5 EXAMPLE IX Water to 1 htre' Potassium palladous dichloride46 g./l. g./l. Pd).

bath should be operated at a current density Of Ethylene diamine tetra-acetic acid 8() g 1 12 amps/sq. ft. and at a temperature of from C. to W t t 1 1it 40 C., the most satisfactory results being obtained at 20 Th 6th 1 ne diamine t t t d a temperature of 30 C. The pH of this bath Was adwith g g f and the g fg i gz 3 32531 3; justed 8 to b th justed to 9.6 with the addition of ammonia.

If deslmd the panadlum m the aboye a The bath gave a dull deposit of a thickness of 0.00018 may be increased to 15 m.wh1ch Case llmght de inch when operated at a current density of 6 amps/sq. posits of a thickness of mch are obtainable by ft. and atemperature of C. The cathode efliciency was the use of a current density of 18 amps/ sq. ft. 90%

EXAMPLE V EXAMPLE X Palladium diam 3)2 Palladium diammino-chloride Pd(NH Cl 15.9 g./l.

21.7 g./1. (=8 g./l. Pd).

30 Ethylene diamine tetra-acetic acid-80 g./l. Ammonium f t l()() /1 Water to 1 litre. Water to 1 litre.

The ethylene diamine tetra-acetic acid vilas g fi i The palladium diammino-chloride was dissolved in amwith ammonia to form the ammonium sat an t e pa ladium salt dissolved in ammonia. The pH of the bath 3 1911311121 and the p H of the final Solution was adjusted to was adjusted to 8.5. bath d H gave a u deposlt of a th1ckness of 0.00017 The bath Should be operated at Cuarrent denslty of 6 inch when operated at a current density of 6 amps/sq. amps/Sq at a temperature of cathode ft. and a temperature of 30 C The cathode efficiency efficiency is 59% and a bright deposit of a thickness of of the bath was 86% 0.00012 inch is obtainable. 40

EXAMPLE XI EXAMPLE VI Palladium tetrammlno nitrate Pd(NH (NO 27.8 Palladium d1amrmno-d1n1tr1te Pd(NH (NO 24 g./l. AII11110Ili11II1PXa1at?/5O Ethylene diamine tetraacetic acid40.0 g./l. Water to 1 litre. a Water to 1 litre.

The P of this bath was adjusted by addition of The ethylene diamine tetraacetic acid was neutralised mom-a to a Value of with ammonia and the pH of the final solution was ad- A bright deposit of a th1ckness of 0.0001 inch 1s objusted to 75 with dilute nitric acid tainable With this bath when operated at a current density This bath gave a dull deposit of a thickness of 000019 of 12 p q a temPerature of 9 fcathode inch when operated at a current density of 6 amps/ sq. ft. efficiency of 53% being obtained. The article being plated and a temperature of The cathode efficiency was should be agitated. 94%

Bright deposits may also be obtained with baths having EXAMPLE VII 59 the compositions given in the following Examples XII Potassium palladous tetranitrite K Pd(NO 43 g./l. XXI inclusive and using palladium diammino dinitrite (=12. g./l. Pd). as the palladium compound and ammonium formate Ammonium citrate-70 g./1. NH OOCH, as the ammonium salt and when operated Water t 1 litre, under the conditions specified therein.

Example XII XIII XIV XV XVI XVII XVIII XIX XX XXI Palladium in g. per litre 10 14 60 5 12 16 1e 14 14. 10 Ammonium formats, g./l 20 5O 60 80 60 70 60 60 60 pH 9.0 8.0 9.0 8.5 10.0 8.5 9.0 3.5 3.5 8,5 Current density, amps/0 2 18 6 6 12 12 450 120 60 6 Thickness, in 0. 0001 0.0005 0.00015 0.00 18 0.0002 0. 0008 0. 0001 0. 0001 0.001 0. 00015 Cathode efficiency, percent- 65 73 78 70 70 9 20 30 Temperature, C 20 30 30 30 40 30 30 30 30 70 Agitation of the article being plated NO NO N0 N0 N0 NO YES YES YES NO The pH of this bath was adjusted to 9.0 by addition 70 1 g. PdE2-175 g. Pd'(NH (NO The compositions of further plating baths in accordance with this invention and by means of which bright deposits of thickness of about 0.0001 inch may be obtained are given in the following Examples XXII to XXVII inclusive together with the operating conditions in respect of each bath.

8. A method of electrodepositing palladium on a basis metal which comprises electrodepositing the palladium Example No XXII XXIII XXIV XXV XXVI XXVII Salt Grams per litre of salt 80 60 60 80 80 80 Grams per litre of palladium 14 15 10 10 16 as Pd(NHa)2(NO2)2. pH 8. 5 9. 0 8. 0 8. 6 8. 8 8. 5 Current density in amps/ftk- 30 6 30 6 3 12 Thickness in inches 0001 0.0001 0. 00015 0. 0001 0. 00012 0. 00012 Temperature, C 30 30 30 32 37 37 Agiltattign of article being YES NO YES NO YES YES a e Caiizhode efficiency, percent- 53 61 66 60 56 61 1 Ammonium citrate. 2 Ammonium tartrate. 3 Ammonium acetate.

Plating baths in accordance with this invention may be used to electrodeposit palladium onto copper, Phosphorbronze, brass, beryllium-copper, stainless steel, mild steel, nickel or silver or other metals. No particular pre-treatment is necessary, normal cleaning procedures being used.

It will be found that bright deposits up to a thickness of at least 0.001 inch are obtainable with barrel plating, the baths being stable and operable at a low temperature at or near room temperature.

The invention is intended to include within its scope a method of electrodepositing palladium upon a base which comprises immersing the base as a cathode in a plating bath or electrolyte in accordance with the invention and electrolysing the said bath. The invention also includes within its scope any base when plated with palladium by the use of a plating bath or electrolyte in accordance with the invention or by the method of the invention.

What we claim is:

1. A plating bath or electrolyte for the electrodeposition of palladium consisting essentially of water, a palladium compound and an ammonium salt of a weak organic carboXylic acid, the bath containing substantially no ethylene diamine tetraacetic acid and having a pH of between about 7 and about 10.

2. The bath or electrolyte claimed in claim 1 wherein the palladium compound is Pd(NH (NO 3. The bath or electrolyte claimed in claim 1 wherein the palladium compound is Pd(NH (NO 4. The bath or electrolyte claimed in claim 1 wherein the ammonium salt is ammonium tartrate, ammonium oxalate, ammonium citrate or ammonium formate.

5. The bath or electrolyte claimed in claim 1 and having a pH from about 8 to about 9.

6. The bath or electrolyte claimed in claim 1 wherein the palladium compound is palladium chloride.

7. A method of electrodepositing palladium which comprises electrolyzing a bath or electrolyte consisting essentially of water, a palladium compound and an ammonium salt of a weak organic carboxylic acid, the bath containing substantially no ethylene diamine tetraacetic acid and having a pH between about 7 and about 10.

on the basis metal from a bath consisting essentially of water, a palladium compound and an ammonium salt of a weak organic carboxylic acid, said bath containing substantially no ethylene diamine tetraacetic acid and having a pH between about 7 and about 10.

9. The method claimed in claim 8 wherein the palladium compound is Pd(NH (NO 10. The method claimed in claim 8 wherein the palladium compound is Pd(NH (NO 11. The method claimed in claim 8 wherein the palladium compound is palladium chloride.

12. The method claimed in claim 8 wherein the ammonium salt is ammonium tartrate, ammonium oxalate, ammonium citrate or ammonium formate.

13. The method claimed in claim 8 wherein the pH is between about 8 and 9.

14. The method claimed in claim 8 wherein the electrodeposition is conducted at a bath temperature of 15- C. and a current density of 1 to 500 amps/R References Cited UNITED STATES PATENTS 2,773,818 12/1956 Moy et al. 20449 3,376,206 4/1968 Kahan et al 20447 1,779,436 lO/ 1930 Keitel 20447 1,921,941 8/1933 Powell et al. 20447 2,027,358 l/l936 Powell et al. 20447 2,057,475 10/ 1936 COhn 20447 2,915,406 12/1959 Rhoda et a] 106-1 3,130,072 4/1964 Duva et a1 1061 XR 3,235,392 2/1966 Miles 106-1 3,274,022 9/1966 Rhoda 106--1 3,285,754 11/1966 Hopkin 106--1 3,264,199 8/1966 Fassell et all. 20438 3,303,111 2/1967 Peach 20438 3,290,234 12/1966 Parker et al. 20447 FOREIGN PATENTS 564,088 11/ 1932 Germany. 25,564 12/ 1935 Australia.

GEMLD L. KAPLAN, Primary Examiner 

